This application claims the benefit of Japanese Applications Nos. 9-274173 and 9-291807 which can hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a projection exposure method used when a mask pattern is transferred onto a substrate such as a wafer in a lithography step for manufacturing, for example, a semiconductor device, an image pick-up device (CCD and the like) and a liquid crystal display device and a thin film magnetic head and a projection exposure apparatus, and more particularly suitable used for a scan exposure type projection exposure apparatus such as step and scan system which comprises a correction mechanism for an image formation characteristic and scans a mask and a substrate in synchronization with a projection optical system to perform exposure.
2. Related Background Art
In the projection exposure apparatus which transfers a reticle pattern as a mask onto a wafer, a glass plate or the like coated with resist through a projection optical system, an exposure must be performed in a state where a high image formation characteristic is always kept. As one factor which exerts influence on the image formation characteristic, there has been thermal deformations of a reticle and optical elements of the projection optical system due to an irradiation of exposure light. In order to correct the change of the image formation characteristic resulting from the thermal deformation of the reticle by the exposure, various propositions have been heretofore made. For example, in Japanese Patent Application Laid-open No. Heisei 4(1992)-192317, a technology was proposed, in which the distribution of the quantity of deformation on a pattern plane of a reticle is computed, and the change of the image formation characteristic caused by this deformation is corrected either by driving parts of lens elements of the projection optical system toward an optical axis or by inclining them relative to the optical axis.
Furthermore, full-field type projection exposure apparatuses, that is, steppers, have been heretofore widely used. In order to perform a transfer for a reticle pattern of a large area with a high precision without increasing a size of the projection optical system, scan exposing type projection exposure apparatuses (scan type exposure apparatuses) such as a step and scan system in which the reticle and the substrate are exposed in synchronization with the projection optical system have been lately become of major interest. Also concerning the correction of the image formation characteristic due to irradiation of exposure light in this scan type exposure apparatus, a technology was proposed, in which the quantity of changes of the image formation characteristic of the projection optical system due to the irradiation is corrected by using the correction method employed in the case of the full-field type exposure apparatus, in Japanese Patent Application Laid-open No. Heisei 6(1994)-291016 and U.S. Pat. No. 5,721,608 related to this Japanese Patent Application Laid-open.
The correction method of the image formation characteristic of the scan type exposure apparatus uses almost the technology to which a system devised for the full-field type apparatus is applied. A correction method considering the change of the image formation characteristic of the whole of the apparatus which includes the reticle and the projection optical system particular to the scan type exposure apparatus, due to irradiation of exposure light, has not been existed.
However, an original pattern illustrated in the reticle used in the scan type exposure apparatus has a large area equal to that of the reticle for use in the full-field type exposure apparatus or an area larger than that. The entire surface of the original pattern is sequentially illuminated in a slit-shaped illumination region during the scan exposure. On the contrary, since the projection optical system is made to become a state where it is always irradiated in the slit-shaped illumination region asymmetrically, in a computing method concerning the quantity of the thermal deformation of the reticle and projection optical system and in a correction method of the corresponding image formation characteristic, the difference occurs naturally. Moreover, influences on the projected image formed on the wafer are different between the case of the thermal expansion of the reticle and the case of the thermal expansion of the projection optical system.
Furthermore, also in the full-field type projection exposure apparatus, the line width of the pattern to be subjected to a projection exposure has been recently finer more and more, and it has been required to correct the image formation characteristic more precisely.
A first object of the present invention is to provide a projection exposure method which is capable of correcting an image formation characteristic with a high precision.
A second object of the present invention is, especially in a scan type exposure apparatuses, to provide a projection exposure method which is capable of precisely obtaining the quantity of a change of the image formation characteristic, either due to an exposure light absorption of a projection optical system or due to a thermal deformation of a reticle, correcting the image formation characteristic according to the quantity of the change of the image formation characteristic with a high precision, and transferring a pattern image of the reticle onto a wafer with a high precision.
A third object of the present invention is to provide a projection exposure apparatus which is capable of embodying such projection exposure method.
A projection exposure apparatus of the present invention comprises a projection optical system for projecting a mask pattern onto a photosensitive substrate; a plane-parallel plate disposed on the photosensitive substrate side of the foregoing projection optical system, substantially perpendicular to an optical axis of the foregoing projection optical system; and an adjustment device for adjusting either an inclination angle of a normal line to the foregoing plane-parallel plate relative to an optical axis of the foregoing projection optical system or an inclination direction of the foregoing plane-parallel plate with respect thereto.
According to the preferred embodiment of the present invention, the projection exposure apparatus further comprises an illumination optical system for changing a size or shape of a secondary light source according to the foregoing mask pattern, wherein the foregoing adjustment device adjusts at least one of the inclination angle and inclination direction of the foregoing plane-parallel plate in response to the change of the foregoing secondary light source.
According to another embodiment of the present invention, in a projection exposure apparatus which exposes a photosensitive substrate by a pattern of a mask, provided is a projection optical system which includes a plurality of optical elements arranged along an optical axis substantially perpendicular to the mask and the foregoing photosensitive substrate, and a plane-parallel plate arranged on the foregoing photosensitive substrate side; and an adjustment device for adjusting an aberration of the foregoing projection optical system by moving the foregoing plane-parallel plate in response to a change of exposure conditions of the foregoing photosensitive substrate.
Furthermore, according to a preferred embodiment of the present invention, the foregoing adjustment device adjusts a decentration coma aberration of the foregoing projection optical system by relatively inclining the plane-parallel plate relative to a plane perpendicular to an optical axis of the foregoing projection optical system without substantially rotating the foregoing plane-parallel plane.
Still furthermore, according to a preferred embodiment of the present invention, in order to adjust at least one of the aberration other than the decentration coma aberration, projection magnification and focus position of the projection optical system, the projection exposure apparatus further comprises a driving instrument for driving at least one of the plurality of optical elements of the foregoing projection optical system.
Still furthermore, according to a preferred embodiment of the present invention, the projection exposure apparatus further comprises an illumination optical system for changing at least one of the size and shape of a secondary light source in response to the pattern of the foregoing mask; and an aperture diaphragm for allowing a numerical aperture of the foregoing optical system to be variable, wherein exposure conditions of the foregoing photosensitive substrate include at least one of the size and shape of the foregoing secondary light source, a sort of the pattern on the foregoing mask, and an numerical aperture of the foregoing projection optical system.
Furthermore, according to another embodiment of the present invention, in a projection exposure apparatus which exposes a photosensitive substrate by a pattern of a mask, provided is a projection optical system which includes a plane-parallel plate arranged along an optical axis substantially perpendicular to the foregoing mask and the foregoing photosensitive substrate; and a driving mechanism which inclines the foregoing plane-parallel plate relative to a plane perpendicular to an optical axis of the foregoing projection optical system.
Still furthermore, according to a preferred embodiment of the present invention, the projection exposure apparatus of the present invention further comprises a stage system which synchronously moves the foregoing mask and the foregoing photosensitive substrate at a speed ratio in response to a projection magnification of the projection optical system, wherein the foregoing photosensitive substrate is subjected to a scanning exposure by the pattern of the foregoing mask, by driving the foregoing stage system.
A first projection exposure method of the present invention which exposes a photosensitive substrate by a pattern of a mask through a projection optical system, comprises: a first step for changing a light intensity distribution on a pupil plane of the foregoing projection optical system of a beam of light which is emitted from a secondary light source and passes through the foregoing mask; and a second step for moving a plane-parallel plate in response to a change of the foregoing light intensity distribution, which is disposed on the photosensitive substrate side of the foregoing projection optical system.
Furthermore, according to a preferred embodiment of the present invention, in the foregoing first step, one of a size and a shape of the secondary light source is changed in accordance with the pattern of the foregoing mask.
Still furthermore, according to a preferred embodiment of the present invention, in the foregoing second step, the foregoing plane-parallel plate is relatively inclined relative to a plane perpendicular to an optical axis of the foregoing projection optical system without substantially rotating the foregoing plane-parallel plate and a decentration coma aberration of the foregoing projection optical system is adjusted.
A second projection exposure method according to the present invention in which by moving a mask and a substrate synchronously a pattern image of the mask is transferred onto the substrate through a projection optical system, at least one of the position of at least one of optical elements of a projection optical system in an optical axis direction, the inclination angle of at least one of the optical elements thereof in the optical axis direction, the relative scanning speed of the mask and substrate, and the parallelism of the mask and substrate in a scanning direction is adjusted before a scanning exposure or during the scanning exposure, so as to correct an image formation characteristic.
According to the projection exposure method of the present invention, before the scanning exposure or during the scanning exposure the position and inclination angle of at least one of the optical elements of the projection optical system is adjusted, whereby a magnification error of the projection optical system, a predetermined distortion thereof and the like are corrected. Moreover, by adjusting the relative scanning speed of the mask and the substrate, a magnification error of its projection image in the scanning direction can be corrected. By adjusting the parallelism of the mask and the substrate in the scanning direction, a parallelogram-shaped distortion for example, that is, so called a skew error, can be corrected. Particularly, if these adjustments are carried out during the scanning exposure, it is possible to cope with a partial thermal deformation of the mask in the scanning direction.
In a third projection exposure method of the present invention in which by moving a mask and substrate synchronously a pattern image of the mask is transferred onto the substrate through a projection optical system, with regard to a change of an image formation characteristic due to a thermal deformation of the mask, its component in a scanning direction is corrected by adjusting a relative scanning speed of the mask and the substrate, and its component in a non-scanning direction is corrected by adjusting a projection magnification of the projection optical system.
According to such projection exposure method of the present invention, in the case where the mask is thermally expanded in the scanning direction, a scanning speed for the substrate is made to be slower than a reference speed determined by multiplying a scanning speed for the mask with the projection magnification of the projection optical system, whereby a magnification only in the scanning direction is corrected. On the other hand, in the case where the mask is thermally expanded in the non-scanning direction, that is, a direction perpendicular to the scanning direction, the projection magnification of the projection optical system is adjusted and the relative scanning speed of the mask and the substrate is adjusted so as to cancel it, whereby a magnification in the non-scanning direction is corrected.
In this case, by obtaining the quantity of heat absorption of the mask based on a thermal movement of the mask created outside a pattern region and a pattern existing rate of the mask, the quantity of the thermal deformation of the mask should be computed from the quantity of the heat absorption. With the consideration as to the thermal movement outside the pattern region and the pattern existing rate, the quantity of the thermal deformation of the mask can be obtained with a high precision, whereby the change of the image formation characteristic due to the thermal deformation can be corrected with a high precision in response to the obtained quantity of the thermal deformation of the mask.
In a fourth projection exposure method of the present invention in which by moving a mask and a substrate synchronously a pattern image of the mask is transferred onto the substrate through a projection optical system, a blind mechanism capable of adjusting a width of an illumination region of the mask is provided, and the blind mechanism is driven in accordance with a difference of the magnification changes of pattern images of the mask in scanning and non-scanning directions, which are formed on the substrate, whereby a contrast of a projection image is corrected.
According to such the projection exposure method of the present invention, if the width of the illumination region on the mask is made to be large in any of the scanning and non-scanning directions, an illuminance on the substrate in any of those directions becomes high. On the contrary, if the width of the illumination region thereon is made to be small, the illuminance in any of those directions becomes low. Moreover, if the illuminance is even on the mask, the illuminance on the substrate becomes lower, as the projection magnification becomes higher. As the projection magnification becomes lower, the illuminance on the substrate becomes higher. Therefore, when the magnifications in the scanning and non-scanning directions are different, the width of the illumination region is changes through the blind mechanism so as to cancel the difference, whereby the illuminances on the substrate in the scanning and non-scanning directions are kept uniform. As a result, contrast unevenness of the projection image can be removed.
In a fifth projection exposure method of the present invention in which by moving a mask and a substrate synchronously a pattern image of the mask is transferred onto the substrate through a projection optical system, a light transmission window of the projection optical system for use in a transmission rate measurement is provided on a mask stage for mounting the mask, and the transmission rate of the projection optical system is measured through the light transmission window.
According to such projection exposure method, by measuring the transmission rate of the projection optical system through the light transmission window on the mask stage, the change of the image formation characteristic of the projection optical system due to an exposure light absorption can be obtained, so that the image formation characteristic can be corrected based on the change thereof with a high precision.
In this case, two light transmission windows should be located interposing the mask therebetween so as to be separate from each other in the moving direction of the mask. Since either of the two light transmission windows can be used according to the scanning direction of the mask, a measurement efficiency is kept high.
In a sixth projection exposure method of the present invention in which an image of a pattern of a mask is transferred onto a substrate through a projection optical system, by driving a plurality of optical elements of the projection optical system individually, an image formation characteristic of the projection optical system is corrected, the projection optical system comprises a first plane-parallel plate on its substrate side, and the first plane-parallel plate is driven in a direction of an optical axis, whereby a predetermined image formation characteristic is corrected.
According to such projection exposure method of the present invention, by combining the drive of the plurality of optical elements of the projection optical system with the drive of the first plane-parallel plate thereof, various kinds of image formation characteristics can be corrected.
In this case, the projection optical system should comprise a second plane-parallel plate having a surface subjected to a predetermined roughening processing should be provided on its mask side, in order to correct a residual component of its aberration. It is possible to correct the remaining distortion by the second plane-parallel plate.
Moreover, an example of a structure may be adopted, in which the mask is illuminated by a beam of light from a secondary light source, and by driving the first plane-parallel plate every time when at least one of the size and shape of the secondary light source is changed, a decentration coma aberration of the projection optical system is corrected.
Furthermore, in the case where a ArF excimer laser is used as the exposure light source, it should be desirable that an atmosphere within the projection optical system is substituted with inert gas such as helium gas or nitrogen gas. In this case, in the case where the atmosphere within the projection optical system is substituted with inert gas, since oxygen showing a absorption band close to the wavelength (193 nm) of the ArF excimer laser light scarcely exists, a transmission rate for the exposure light increases. Similarly, also in the case where the atmosphere within the projection optical system is substituted with nitrogen gas, since the nitrogen gas hardly absorbs the ArF excimer laser light, the transmission rate for the exposure light increase.
Particularly, in the case where the atmosphere within the projection optical system is substituted with the inert gas, since a change of the atmospheric pressure affects scarcely on the inside of the projection optical system, the change of the image formation characteristic due to the change of the ambient pressure within the projection optical system can be controlled.
Furthermore, it is desirable that the ambient pressure within the projection optical system is measured and the image formation characteristic is corrected based on the measurement result. Since the image formation characteristic is made to change also by the change of the ambient pressure within the projection optical system, the image formation characteristic can be corrected with a higher precision by performing the correction in accordance with the change of the ambient pressure within the projection optical system.
Next, in a projection exposure apparatus of the present invention in which a pattern of a mask is transferred onto a substrate through a projection optical system, the projection optical system comprises a plurality of optical elements arranged between the mask and the substrate along an optical axis; a first plane-parallel plate disposed on the substrate side; and a second plane-parallel plate disposed on the mask side, wherein provided is a driving device which drives the first plane-parallel plate in order to adjust a decentration coma aberration of the projection optical system, and drives at least one of the plurality of optical elements without relatively moving the second plane-parallel plate with respect to the mask, in order to adjust at least one of the aberration other than the decentration coma aberration, projection magnification, and focus position of the projection optical system.
According to such projection exposure apparatus of the present invention, a sixth projection exposure method of the present invention can be embodied. In this case, the driving device moves at least three optical elements of the projection optical system, as an example. Thus, the projection magnification, the distortion and the astigmatic aberration can be adjusted.
It is also satisfactory that the driving device drives at least four optical elements of the projection optical system. Thus, the projection magnification, the distortion, the astigmatic aberration and the coma aberration can be adjusted.
Furthermore, it is also satisfactory that the driving device drives at least five optical elements of the projection optical system. Thus, the projection magnification, the distortion, the astigmatic aberration, the coma aberration and the spherical aberration can be adjusted.
In order to adjust the field curvature of the projection optical system, it is desirable that an adjustment device for changing the refractive index in at least one of a plurality of spaces formed by the mask and the plurality of optical elements is further provided.
Furthermore, when at least one of the size and shape of a secondary light source is changed in accordance with the pattern of the mask in an illumination optical system, it is desirable that at least one of the plurality of optical elements and the first plane-parallel plate is moved in response to the change of one of the size and shape of the secondary light source.
Furthermore, the projection optical apparatus further comprises a measuring instrument for measuring the ambient pressure in the projection optical system, and it is desirable that the driving device thereof moves at least one of the plurality of optical elements and the first plane-parallel plate in response to the change of the ambient pressure in the projection optical system.
Furthermore, it is desirable that the driving device relatively inclines the first plane-parallel plate relative to an image plane of the projection optical system without substantially rotating the first plane-parallel plate and adjusts a decentration coma aberration of the projection optical system.
Furthermore, it is desirable that the surface of the second plane-parallel plate is uneven so as to correct a symmetrical aberration of the projection optical system.
Furthermore, in order to perform the scanning exposure of the pattern of the mask onto the substrate, it is desirable that a stage system for synchronously moving the mask and the substrate is provided. This means that the present invention is applied to a scan exposing type projection exposure apparatus.